(1) Field of the Invention
The present invention relates to a semiconductor leakage current detector and a leakage current measurement method for detecting a bit line leakage current of a flash memory and the like at high-speed and for executing on-chip trimming of a reference voltage, to a semiconductor leakage current detector with a voltage trimming function and a reference voltage trimming method, and to a semiconductor integrated circuit thereof.
(2) Description of the Related Art
In recent years, non-volatile memories such as a flash memory and an EEPROM are arranged as a large storage capacity memory array using fine memory cells in addition, as memory cells are finely processed, it has become essential that a non-volatile memory is equipped with a reference voltage source that supplies an accurate internal voltage necessary for rewrite and read-out operations.
One of the problems the recent non-volatile memories are facing is the increase in the leakage current of bit lines due to the development of large storage capacity memory array. This problem particularly results from the increase of the leakage current (bit line leakage current) in each memory cell caused by the fine processing, and the increase in the number of memory cells for each bit line. The increase in the bit line leakage current has an impact on the read-out operation of the memory cell, and degrades the control accuracy of the threshold value of the memory cell and the reliability of the data retention characteristic and the like. The threshold value control process (hereinafter, referred to as a program) of the non-volatile memory cell is controlled by the determination of the width and height of a program pulse and the threshold value, in other words, the repetition of a determination operation (referred to as verify) of the cell current. In the verify operation, the bit line leakage current causes the erroneous determination of the cell current with an error which is as much as the leakage current, results in the excess or insufficiency of charge injection, and impedes the normal threshold value control of a memory cell.
To realize the high reliability of the memory, it is necessary that bit lines in which a leakage is detected during a device test be the object for redundancy replacing, and the relevant device be excluded as a defective device. With regard to such bit line leakage current, a leakage current down to several μA is detected by a sense amplifier which is used for read-out operation.
The measurement of the bit line leakage current by a sense amplifier is described in Patent Reference 1 (Japanese Laid-Open Patent Application No. 06-251593). In addition, a direct measurement method of the leakage current is described in Patent Reference 2 (U.S. Pat. No. 6,201,747 B1); the measurement of the threshold value of a cell is described in Patent Reference 3 (U.S. Pat. No. 6,370,061 B1); the measurement of the on-chip current is described in Patent Reference 4 (United States Patent 2005/0229050 A1).